1. Field
One or more embodiments relate to a rotor of a brushless (BL) motor, and more particularly, to such a rotor of a BL motor, which minimizes the transfer of an electromagnetic vibration and a noise to a rotary shaft thereof, and enables a torque of the rotary shaft to be normally transferred to cylindrical ring magnet assembly.
2. Description of the Related Art
In general, a conventional rotor of a BL motor employs a permanent magnet, and is constructed such that a rotary shaft is coupled to a rotor core using a ferromagnetic material or a steel plate so as to form a magnetic circuit structure of a permanent magnet.
Such a motor rotor entails a problem in that when a permanent magnet rotor interacts with a rotating magnetic field of an armature to generate a torque, electromagnetic cogging, torque ripple or vibration due to electromagnetic interaction always occurring in an air gap between the rotor and the armature is directly transferred to the rotary shaft for transmission to another load side or is amplified to thereby induce serious mechanical noises such as resonant noises.
A method may be used in which a sound-absorbing resin such as rubber or silicon resin is interposed between the ferromagnetic core and the rotary shaft to interrupt noise and vibration transferred through the permanent magnet and the ferromagnetic core in order to reduce the vibration and noise of the rotor of a BL motor.
In this case, the ferromagnetic core having a predetermined area is necessary to minimize a resistance of the armature and the magnetic circuit of a C-type permanent magnet.
Further, the use of the ferromagnetic core makes it hard to significantly reduce the weight of the rotor. The ferromagnetic core still serves as a medium for transferring cogging, torque ripple, noise or vibration occurring in the rotor, and thus there is a limitation in interrupting the noise and vibration only using the sound-absorbing resin disposed around the rotary shaft.
In addition, the conventional permanent magnet rotor as constructed above has a shortcoming in that a high-strength adhesive must be used to combine the permanent magnet and the ferromagnetic core and the weight of the rotor is unbalanced in the course of bonding permanent magnets divided into at least two pieces.
Accordingly, an aspect of an embodiment has proposed a rotor of a BL motor in which a cylindrical permanent magnet having a magnetic circuit embedded therein is used to eliminate the need of the ferromagnetic material used for forming a rotor magnetic circuit allowing for passage of a separate magnetic flux of a permanent magnet.
The rotor of a BL motor using the cylindrical ring magnet assembly proposed by an aspect of an embodiment can be applied to a small-capacity motor such as a stepping motor or a micro motor.
However, such a rotor of a BL motor employing the cylindrical ring magnet assembly encounters a problem in that the bonding force between a high-strength engineering plastic member securely mounted around the rotary shaft and a sound-absorbing resin element formed by injection-molding a sound-absorbing resin around the high-strength engineering plastic member is so weak that in case of a power BL motor requiring several tens of W or more, a torque is normally transferred to the rotary shaft or the cylindrical ring magnet assembly to cause the rotary shaft or the cylindrical ring magnet assembly to be idled, thereby making commercialization of the motor is hard.